Mauna Loa keeps paradise interesting. It has erupted 33 times since 1843, with large eruptions happening on average once every 8 years. Over that time it has covered its slopes with 4 km3 of new lava. But those are just the most recent stirrings. Its older lava flows cover over half of the island of Hawaii. But after the large eruption in 1950, Mauna Loa became remarkably quiet. There have been only two eruptions since, one of which (1975) lasted less than one day and was the second smallest eruption of the 20th century. There was one significant eruption in 1984, but nothing since. But now the largest volcano on Earth is stirring. Inflation shows that magma is accumulating, just south west of the peak. Earthquakes are a daily occurrence and HVO has raised the alert level. There is trouble brewing in paradise.

Mauna Loa is the world’s second tallest volcano on Earth, after Mauna Kea. It started 5 km below the sea, taking perhaps a million years to reach its current height of 4.17 km above sea level. The total height, from base to summit, is therefore over 9 km, more than Mount Everest. To compare, the highest volcano on Earth is Ojos del Salado, on the Chile/Argentina border, which reaches 6,893 m above sea level. Mauna Loa is slightly cheating since the part that is under water benefits from the upward pressure from the water – it floats a bit. I can correct for this, and calculate how high a mountain would be that has the same pressure at its base, without the aid of water: this reduces Mauna Loa by 1800 m, and gives an equivalent height of 7200 m, almost the same as Ojos de Salado. This may not be entirely accidental. There is only so much weight a rock can bear, and both volcanoes will consist of very similar types of rock at their base. Rocks at the bottom, 9 km below the summit, are in danger of being crushed by the weight. On Mars, gravity is three times less and the same weight corresponds to a mountain three times taller – 22.5 km tall. In fact, Olympus Mons stands 22 km above the surrounding plain, almost exactly this number. So it seems this is indeed about the tallest a volcano can get. Mauna Loa and Mauna Kea are almost the same height, differing by only 24 meter. They are running into their limits.

Although it is slightly lower, Mauna Loa is a lot bigger than Mauna Kea. Mauna Loa is a shield volcano: its fast flowing lava has spread far, building a large mountain with a shallow slope. It is much wider at its base than Mauna Kea, has much more volume and therefore much more mass. Mauna Loa, the largest volcano on Earth, is so large, it is very hard to see. You can’t see it above the horizon: it IS the horizon. I remember reading the story of someone in Africa trying to chase an elephant out of their garden at night. In the flash light she failed to see any elephant, just the greyish sky. Only than did she realize the sky was the elephant, so large the eye couldn’t see it. Mauno Loa is this proverbial elephant. The only place from where you can get a good feeling for its tremendous size is from the summit of Mauna Kea (not an easy place to get to either.) From here, at night sometimes you can see the distant, angry eye of Pu’u’O’o, but in the day Mauna Loa dominates the sky line. (Unexpectedly for an astronomical observatory, you can’t see the stars that well from Mauna Kea. It is too high and the eye and the brain are badly affected by the lack of oxygen. You become half blind and too dim to realize.)

Mokuaweoweo crater, with south west rift in the foreground

The top of Mauna Loa has its crater, called Moku`aweoweo Caldera. It consists of three partly overlapping craters, of which the central one is the largest. Together they are 6 by 2.5 km in size. The caldera isn’t that old. It formed because of a large flank eruption which emptied the shallow magma reservoir. This was the eruption which formed the Pana`ewa flow field, which Hilo is build on.

Mauna Loa is a very elongated mountain, much longer in the south west-north east direction. In fact, the name Mauna Loa means ‘long mountain’. The long ridge follows a double rift zone. There is a caldera at the top (showing the mountain used to be a little higher); the rifts extend from the caldera towards the south west and towards the east, running from the south eastern point of Hawaii to (almost) Hilo, a distance of close to 100 km. The south west rift bends by 40 degrees where it reaches an altitude of 2400 m. At this point a number of eruptions have build a satellite shield.

Mauna Loa eruptions tend to begin near the summit, but quickly migrate to the rift zones, down slope. Both rifts can erupt anywhere along their length. Individual rift eruptions can occur along a section as short as tens of meter, to a staggering 20 km (as happened during the large 1950 eruption). Individual eruptions typically last a week, erupt 0.2 km3 of lava and cover 20 km2. The lava moves fast, covering up to 5 km per hour on the steepest slopes, and can reach the sea (on the west and south side, at least), in less than a day.

Map showing areas covered by `a`a lava flows erupted during the eruption of Mauna Loa between March 24 and April 15, 1984. Source: HVO

The 1984 eruption is a good example. It began three years earlier, with slowly increasing earthquake activity, culminating in an M6.6 event. About 5 months after this, 25 March 1984, the eruption began, after 2 hours of tremors, initially at the summit, but within hours the eruption migrated first to the south west rift zone, changed its mind and moved to the north east rift zone. A few hours later, lava curtains erupted 7 km from the summit, and later that day, the eruption moved to a 2 km section 10 km from the summit. From here lava flows quickly advanced to Hilo. Eventually the flow reached a length of 30 km, coming to within 7 km of Hilo. As the eruption diminished, the active lava stayed closer to the point of eruption. After some tense days, the eruption ended on April 15.

Hawaiian Archipelago: trail of a hot spot

Hawaii is at the end of a long chain of islands and sea mounts. Close to Hawaii are the Windward islands, or Hawaiian archipelago. Further away are the Leeward islands, terminating near Midway. Beyond that, the chain becomes a series of sea mounts, which makes an angle of 120 degrees with the other chain: these are called the Emperor sea mounts (named after Japanese emperors). The mounts get progressively older further from Hawaii, with the oldest one about 80 million years. The chain terminates at the Obruchev Rise, very close to the Aleutian subduction trench, where it meets Kamchatka. There may have been more, older sea mounts, now subducted into oblivion.

The Hawaiian chain is the type specimen of a hot spot chain. The hot spot is supposed to have been stationary or near stationary, while the Pacific plate drifted over it. The sharp bend in the chain shows a sudden change of direction of the Pacific plate, about 45 million year ago. Previously, the plate was going north, but now it is moving to the north west. What caused this change? That is not really known. It happened at about the time India collided with Asia, and perhaps this is related although that was quite a distance away. It may also have been caused by the onset of subduction along the Asian plate boundary. After the change of direction, for a few million years no islands were formed.

Hot spots may come from plumes deep into the mantle, or they can be shallower, affecting mainly the upper mantle. Opinions differ. In the case of Hawaii, seismographs, used to map out the mantle, have detected the hot region to 1500 km depth, perhaps more. That is half the depth to the core-mantle boundary. It seems likely it extends to the bottom of the mantle. It came from the deep. But other data do not agree, and a more recent study has only found a pancake of heat, underneath the crust, not extending into the deep.

In any case, not all the lava it erupts comes from the deep mantle. It seems that over time, Mauna Loa has erupted a decreasing fraction of 3He, and that is a sign that a fraction of recycled crust is being included in the magma. Perhaps as the hot spot is moving away (and Mauna Loa is no longer directly over it, as it was when it began), the magma includes an increasing amount of shallower melt.

How and where did the hot spot get started? Its origins have sadly been lost in the subduction trench. Or perhaps not. Could the hot spot have started at the Obruchev Rise? The Rise is near an old spreading centre, abandoned in the Cretaceous when the centre jumped north. The ridge was at the western edge of the Fallaron plate, which has since largely been subducted underneath America. This puts the hot spot, at its earliest known location, directly underneath this spreading ridge. Much like Iceland! Did the spreading centre start the plume? Or did the plume split the plate? This is solidly in the realm of speculation. But it is interesting to think of tropical Hawaii starting off like Iceland. Perhaps there is hope for Reykjavik.

During its 80 million year history, the eruption rate has been remarkably constant, at about 0.015km3 per year. For comparison, over the past 200 years the eruption rate has been about 0.023km3 per year from Mauna Loa. Kilauea’s eruption rate should be added, which doubles the amount. So the current rate of activity is a bit above average for the hot spot.

Science

Volcanoes provide a very temporary surface and are not the best place to build expensive structures. A good example was the Etna volcano observatory, build too close and unfortunately destroyed by the lava they were trying to observe. They wisely relocated to Catania, for safer viewing. It is surprising to find a scientific institute located near the top of Mauna Loa, and even more surprising that it is not there to study the volcano. The Mauna Loa Observatory studies our air and our Sun – not the shaky ground underneath their feet.

The Observatory is located 5 km north of the summit, 700 meter below it. It is so high up in order to stay away from any pollution (natural or otherwise) coming up from below. The inversion layer in the atmosphere normally keeps that locked up. The air comes in from the sea, again as clean as anywhere on Earth. It is an ideal pace to measure how our air is changing. Since 1956 the amount of CO2 in our atmosphere has been measured. There are several places around the world where this is done, but Mauna Loa has the cleanest record. The buildings, offices and domes are build on stark, black lava fields and even after 50 years, gives an impression of a temporary incursion in an unforgiving land. The total lack of any vegetation is an advantage, as plants affect the local CO2. The famous Keeling curve, showing how rapidly we are changing our atmosphere, is measured here, a monument to our fragility and willingness to take inordinate risks. It fits the environment, but if Mauna Loa were to erupt this direction, the scientists may only have an hour to get away. There is also a solar observatory here. In general, only astronomers put their most expensive instruments on top of active volcanoes. A certain disregard of the world they live in may play a role. There is a massive astronomical observatory on Mauna Kea. Again, their only access road goes over the recent flows from Mauna Loa. One could question the wisdom of building the one escape route where it is most likely to be cut off.

The Keeling curve

The mid-life crisis of Mauna Loa

I mentioned that Mauna Loa seems to be losing its hot spot. How do we know? Part of the evidence comes from the changing isotopes, the reducing fraction of 3He compared to 4He. But there is a more direct indication. Mauna Loa has stopped growing.

Mauna Loa’s lava covers half of Hawaii, to the coast and into the sea. The eruptions still often reach the sea, at least on the west side of the island, but they only rarely reach the Hilo area, even though this area is entirely build on Mauna Loa’s lavas. Over the past 100,000 years, the lava flows have not been as vigorous and have not reached as far as previously. Still, Hilo should not be complacent. In 1880 lava reached with 2 km of Hilo Bay.

How far lava can flow depends on the cooling rate. The flow stops where the lava solidifies. The higher the flow rate, the slower the cooling (large bodies stay warm for longer), and the further the lava flows reach. This process is very clear in Kilauea. When the eruption rates go up, the lava flows extend, as they did last year. When they decline, lava stays closer to the point of eruption, mostly less than 5 km this year. Holuhraun did the same thing: when the flow began to diminish, the flow field stopped expanding. Lava from Mauna Loa now rarely reaches Hilo Bay, perhaps only once per 4000 year. It mostly stops 5-10 km from Hilo. One flow did cover the entire urban area and the bay, perhaps 1000 year ago, but this one erupted from a vent very close to Hilo to begin with. Most of the lava now flows closer to the rift, and less lava reaches the sea. This makes the mountain grow steeper: it is beginning to enter its post-shield phase. This may be related to the growth of Kilauea, competing with it for lava resources.

The weight of the mountain pushes the crust below down. The whole island subsides, at around 2 mm per year. So far lava deposition has just about kept up with this, but it may not for much longer. The baton is being passed and Mauna Loa will sink.

The 30-year silence of Mauna Loa has coincided with the continuing eruption of Kileauea at Pu’u’O’o. This eruption started in 1984 and is still going. But eruption rates have slowly declined. The central crater of Kilauea shows inflation and this may be due to an ebbing flow through to Pu’u o’o. It is argued that Mauna Loa and Kilauea are separate volcanoes, from two different hotspot tracks, Kilauea connecting to Mauna Kea. This seems less likely, and although the feed systems are not identical, they are not independent either – they are too close together. The question will be settled soon: if they are independent, a Mauna Loa eruption would not affect Kilauea. If there is connection between them, you would see Kilauea changing when Mauna Loa erupts. Will in the future Kilauea take over and rival Mauna Loa in size? Perhaps they really are too close. There is another candidate waiting out at sea, which is more likely to become the next giant.

Towards eruption?

After 20 years, activity underneath Mauna Loa resumed in 2004, with a series of deep earthquakes. The mountain began to inflate at the same time. Things calmed down again, but in 2014 earthquakes moved to shallower levels, and inflation increased. Magma is now accumulating at 3-5 km depth, below the south west rift. Activity is continuing at an elevated but non-critical level: it has all the appearance of building up to an eruption, but it does not appear to be imminent. Will it be a year, five years, longer? After the previous burst, in 2004, nothing happened for a decade. The current episode could equally go off the boiler. But the magma is now shallower, and the inflation more focussed. This is beginning to look as if it is closer to deciding to erupt.

Inflation and earthquake activity at Mauna Loa. Source: HVO

An eruption is likely to start within hours of strong tremors. Initially it will be close to or at the summit, before rapidly migrating. As the current inflation is a little south west, the most likely migration is in this direction. The lava could flow either side of the ridge. For a normal-size eruption, Highway 11 will be cut within one or two days, possibly at several locations if the eruption is large, and lava will flow into the ocean shortly after. Judging from the time line of the various flows since 1843, Kealakekua Bay would seem next but this is guess work – Mauna Loa does not work like that. As the magma chamber empties, the risk of larger, possibly damaging earthquakes increases. The south side of the mountain is prone to slipping and the risk of this increases when the pressure changes. Conversely, earthquakes can also affect internal magma flows and an earthquake can hasten or stop an imminent eruption. The double 1868 earthquake (M7.1, M7.9) disrupted the magma supply for decades.

Purely based on the past record, there is a 50% chance of an eruption within 8 years. I would expect something within a decade, most likely from the south west rift zone. When it happens, it would be advisable to run away, and not, as Hawaiians normally do, run towards the eruption to get a better view. Mauna Loa is not like Kilauea. It is fast and furious, best viewed from a large distance. Paradise can wait.

60 thoughts on “Trouble in Paradise: awakening Mauna Loa”

An Australian will bet on anything. I’ll put US $5 via Paypal to a fund for the person who gets closest to predicting where a future eruption of Mauna Loa will cut Highway 11. My prediction is 2 km south of Pahala on the south east side of the ridge, at the intersection of 2 small creeks.

There are collapses, but perhaps fewer than in steeper volcanoes. Kealakekua Bay formed from a major flank collapse which left debris 100 km out. Remember, though, that over half of the volcanoes is below water: you are looking for evidence down at the sea bottom. Hawaii is estimated to suffer flank collapse about once per half a million year. At the moment, the south side of Kilauea is not entirely stable, and is sliding down at about 1 meter per decade. It seems to be held back by the debris of the previous collapse there, on the sea floor. It survived the M7.9 so can’t be that unstable!

There is also an extinct spreading centre in the NW Pacific that may have had something to do with the changing direction of the seamount chain, as well as the collision of the North American and Asian plates. Lots of suspects.

As for the turning of the hotspot track…I wonder if the Farallon Plate started dragging the entire northern portion of the Pacific plate sideways with it when it began subducting in earnest. Recent models indicate that the plate remained largely intact and relatively shallow as it went under North America (I read that somewhere in relation to the Yellowstone track). That is a lot of mass to be pulling on the oceanic crust remaining above the CSZ, and with tidal forces increasing at depth (as well as convective flow from the mantle pushing on what is in essence a very large sail) the speed of subduction could have increased forming a nifty positive feedback loop, pulling and causing (at the time, a much smaller) Pacific plate to pivot. There appears to be some interesting features on the sea floor that resemble stretch marks to the west and south of the Juan de Fuca plate but north of the equator. And, the plate’s collision had the necessary mass to push up and fold the Rocky Mountains plus the subducted remains of the Farallon plate are suspect as a cause of the Rio Grande Rift. The plate may have subducted at an increasing rate until the tensile strength of the plate could not hold the slab together; it snapped off, sinking. At this point, the plate subduction would have returned to background levels. It and time left us with what we see today.

Secondly, what is keeping the southeast portion of Hawai’i intact? The limited bathymetric information we have southeast of Kilauea shows that it is a fairly steep drop from sea level to 6,500+ meters below. The island from the Great Crack in the WSW around Pahala to north along the ridge holding the Chain of Craters parallel to the coast to Cape Kumukahi seems as if it could slide off relatively easily. The ridge is about 350m ASL – and I don’t care who you are, that is a lot of rock with a very long way to fall. Adding insult to injury, Kilauea just keeps piling on more rock, extending the mass farther out to sea. Eventually the weight could cantilever the whole edge off of the island and trebuchet a wall of water towards the Galapagos and Chile, no?

The south side of Kilauea collapsed 20-30,000 years ago. Apparently the debris from that is helping to keep the current side into place. It is slipping, at 1 meter per decade, but that is a comfortable speed. Yes, when the west side it caused a tsunami in Hawaii with a run-up of 200 meter. Because it is only one point that gives (as opposed to an earthquake that gives way over a long fault), the tsunami would decay quite a bit with distance. Still, you could get 10’s of meters around the pacific if I estimated it right. but it seems a low chance of happening at the moment.

The first thing to search for is what the pacific looked like 80 million years ago! That is far from straightforward: lot of uncertainties. The second thing is if you can find any evidence of the hot spot from before 80 million year ago, at the other side of the spreading ridge (at least where it was at that time). It seems to have no history, coming out of nowhere.

Mauna Loa is gentle effusive….but enromous ammounts of magma are erupted over a short time. and the south part of Big Island is relativly steep and the fluid lava can really get up speed and many housing developments are built directly on earlier lava flows…..and the hazard is quite huge according to Hawaiian volcano obervatory. Current earthquakes are sporadic and not in order. but she is far overdue and keeps inflating soo the next eruption maybe very huge indeed….Very nice nice article! can I share it?

Hawaii is much more build up than it was last time Mauna Loa erupted, and that increases the danger. In the past, there has been enough warning that people could getaway but not so much that they could rescue any possessions. Individual lava channels may be quite narrow by the time they reach the lower slopes, so the number of houses affected may not be so large. Whether the eruption will be large is hard to predict. The biggest risk of that, I think, is if an earthquake were to open up a new magma conduit.

Sakurajima has been largely constipated ever since that seismic crisis a while back. While it still has spurts of its vulcanian explosions, they haven’t been as regular or nearly as frequent as they had been in the past. I tend to believe that during that event, something changed in the system.

I wish there was more accessible instrumentation on Sakurajima, similar to what we get with IMO. While Iceland is very interesting, I feel like Sakurajima is much more interesting and important to pay attention to and monitor. If only we could see the GPS signals here as we can with Iceland..,

Mauna Loa eruptions are often quite voluminious and large…… but the volcano shows diffrent types of effusive vigour. from large fissure eruptions like 1950 s , 1980 s . These eruptions erupts from the Rift Zones and forms huge curtains of lava fountains and you have an enromous flow over the surface. and huge fast flowing lava channels froms that feed fast flowing aa lava flows that advances

to older and more slower eruptions… a large part of Mauna Loa is covered by pahoehoe suggesting earlier tube feed flows that where feed from a summit lava lake and eruptions resembled todays Kilauea.
Mauna Loa is clearly capable of diffrent eruptive vigour.

A possible cycle
A cycle begins during a period of high-standing magma collum at Mauna Loa’s summit. This is seen by near constant lava lake activity and lava overflowing, from which karge sheets of tube feed pahoehoe blanket the northwest and southeast flanks. The last such period of summit activity lasted for about 800 years between 1,200 and 2,000 radiocarbon years ago and was accompanied by frequent smaller eruptions from radial fissures on the northwest rift flank. This period of summit overflows may end when a large flank eruption occurs low on the flanks and robs Mauna Loa of the high-standing magma collum required for shield building.

The sudden lowering of the magma column associated with caldera drainage results in a major change of activity as both rift zones become characterized by frequent large scale eruptive activity (an estimated average of one rift zone eruption each 20-25 years over the past 1,000 years). Sporadic ummit activity probably continues during times of heightened rift activity (as it has during the 19th-20th centuries but all erupted lavas are trapped within the summit caldera and no summit lava lake, and no trace of this activity remains at the surface.The fissure rift eruptions are mouch mouch mouch larger than the summit eruptions in flow rates and forms huge very spectacular eruptions like 1950 s and 1980 s

As stresses increase across the rift zones over time, magma again rises more easily within the edifice, and the caldera is filled. A lava lake appears at Mauna Loa’s summit, pahoehoe sheets are able to overflow the caldera walls, and the cycle begins again.

This includes text from http://hvo.wr.usgs.gov/maunaloa/history/model.html VC aims to quote sources where text or figures are used from elsewhere. It is a plausible model but there is is no reason why this should be strictly cyclical, as it depends on a break-out on the flank which could happen at any time. What they call the cycle sounds more like the recovery period after such an eruption.

Very shallow. Some weeks back there were several similarly shallow sporadic quakes in bb. I wonder about the mechanism. Rocks cracking from deformation? This latest one looks like a twin peak on the drums. Could the great VC brain explain this one to a curious amateur?

The depth is likely due to this being blocking or movement in the caldera lid, which has been ongoing since the onset of the eruption of 2014. Right now, it’s tough to say if the quake is due to the lid dipping (settling), or rising (inflating). Regardless, any movement in the caldera lid will cause earthquakes at a fairly shallow depth.

As for the twin peak, I believe some have proposed that there is a phenomenon where the quake “echoes” a bit as it hits the lower region in the chamber (the plug). This causes some quakes to show up as double peaks, although I’m not sure if this is proven. It could just as easily be two quakes that occur somewhat concurrently..

It now lists two M2.1’s for this morning, between 11 and 0km depth! That is one long crack. There was a further one later at intermediate depth. All htree are inb locations where there hasn’t been much so far.

I remeber being up on Mauna Loa that volcano is insanley huge……. takes up a large part of the Big island
I remember driving up to the co2 observatory and then its a hike to the caldera. It was a january day and the whole mountain was covered by snow…it was amazing…standing at the caldera rim.
I walked inside the caldera, watched smoking fumaroles from the 1949 eruption and the still hot dikes
I even climbed the intra caldera spatter cone.

I wonder in what way you messed with the lava. I have been within 2 meters of the lava and it got too hot for me. These were the break outs at the tip of the lava flow, advancing rather slowly but it set fire to moss well before it touched it.

I went to Kilauea and hiked the active flow field ….. very very long hike!!! and hiked out on the ocean pali where many active leaks from the lava tube system, lava was acessible and I coud go straight to the action and mess around with liquid lava with my walking stick long made of a thick tropical plant stem

Hekla may erupt soonish according to prof Páll Einarsson. The super quick and dirty translation/gist of the story, is that the newest tilt measurments show that there’s a noticable higher pressure going on atm than was needed for the last two eruptions, together with Heklas history in general, this could mean a kablooie at any moment.

Over 77 types of “Erupt now!!” reciepies have been tried. Even stapping with both feet near did not work. Briefly leaving (the country) “to the mercy of the natural powers” had no effect either. This activity has one puzzled, so as insurance Páll Einarssons “issues statement” (actually “old” one, recycled from July 2011).

Do anyone here have an opinion how long the Puu Oo eruption will last? It seems very very well conntected with the deep magma system and Puu Oo even have its own lava lake……suggesting a very very well connected with the deep magma system. I say it will continue for a very long time….beacuse Puu Oo is soo well connected with the main magma system at Kilauea.
The Puu Oo eruption may continue for a very long time being soo well feed
but we will never know…..and I maybe wrong

Depends on what the weak point is! Kilauea has a tendency to do one thing for a long time. there was an eruption in the central crater from 1823 to 1924, essentially continuously. So Pu’u’O’o coul last a long time. But it needs the dyke from the central magma chamber to be unobstructed. Over time, it may become blocked and once lava stops flowing, it solidifies and plugs the channel. The fact that magma has been rising in the central crater suggests the opening to Pu’o’O’o is not as open as it once was. Doesn’t mean that it will stop though. It could last another 20 year, or the lava cold suddenly find another escape route, or an earthquake could block the channel. It is fairly unpredictable, but there is no reason to assume it will stop soon.